(a) Field of the Invention
The present invention relates to a piston in an internal combustion engine for use with an diesel engine, and more particularly, to a piston assembly for use in an internal combustion engine, having a counter-flow thwarting construction therewith, whereby an unwanted combustion of an engine oil together with a fuel, which may occur when the engine oil is introduced into a combustion chamber by an inner pressure being instantaneously generated in the piston moving down during its ordinary reciprocating movements, can be prevented, resulting that an excessive consumption of the lubricant, smoke caused by incomplete combustion and reduction of power can be avoided.
(b) Description of the Related Art
In general, a piston in an internal combustion engine reciprocates within a cylinder, wherein a suction stroke, a compression stroke, an explosion stroke and an exhaust stroke occur generating a power. In order to increase the power, various efforts such as an endeavor to remove the factors that would reduce the power have been attempted.
The power-reducing factors are, e.g., an incomplete combustion occurring when an engine oil is introduced into a combustion chamber to be burnt together with the fuel, an inferiority of an injection nozzle tip, a shortage of the amount of the suction air and a poor air-tight property of the piston ring.
Studies have found that the incomplete combustion caused by the engine oil results in a mass of carbon or soot adhering to a crown of the piston or an external surface of the piston, especially, that a reverse flow of the engine oil or air into the combustion chamber of the cylinder or an introduction of the fuel into an inside of the piston is caused by an internal pressure generated within the chamber near a crank during the reciprocating movement of the piston.
Hereunder, this phenomenon will be described in detail with reference to the accompanying drawings.
FIG. 1a presents a suction stroke of a cylinder where a piston 20 moves down from a top dead point to a bottom dead point and a suction valve V1 is opened simultaneously, introducing air and fuel into a combustion chamber 10a. 
FIG. 1b represents a compression stroke of the cylinder where the piston moves up from the bottom dead point and the suction valve V1 is closed simultaneously, thereby compressing the air and fuel in high temperature and high pressure.
FIG. 1c represents an explosion stroke where the fuel compressed in the high temperature and pressure condition is exploded to be burnt when the piston 20 reaches the top dead point; and FIG. 1d represents an exhaust stroke where an exhaust valve V2 is opened and the piston moves up to the top dead point, resulting that the combustion gas is exhausted out of the combustion chamber 10a. 
As shown in FIGS. 1a to 1d, the piston reciprocating within the cylinder 10 has a plurality of ring grooves 22a, 23, wherein a compression ring 22 and an oil ring 24 are mounted in the ring groove 22a. 
Accordingly, during the reciprocating movements of the piston, the compression ring 22 presses against the internal surface of the cylinder to generate a surface pressure therebetween, providing a pressing pressure in the combustion chamber 10a. The oil ring 24 functions to scratch the engine oil off the cylinder.
In the suction stroke (shown in FIG. 1a) where the piston 20 moves down from a top dead point to a bottom dead point and a suction valve V1 is opened simultaneously, generating a vacuum state in the combustion chamber 10a, a pressure within the piston 20 is sharply increased. For this reason, a reversed flow of air is introduced in a direction indicated with an arrow A in an oil passageway, thereby allowing oil sticking to or remaining on the oil ring 24 and the ring groove 23 to be introduced into the combustion chamber along an internal surface of the cylinder liner.
The oil conversely flown into the combustion chamber sticks to the internal wall of the cylinder liner in a large amount and is further introduced into the combustion chamber in the compression stroke, in a direction indicated with an arrow B, during which the piston 20 moving up scratches up the oil sticking to the internal wall of the cylinder liner. The engine oil introduced into the combustion chamber having a higher level of flash point would hinder the combustion in the explosion stroke (see FIG. 1c), causing the incomplete combustion and would emit smoke in the exhaust stroke (see FIG. 1d).
In the operation of the four cycle engine, since the internal pressure of the piston becomes lower sharply during the exhaust stroke (see FIG. 1d) where the exhaust valve V2 is opened and the piston moves up toward the top dead point, the combustion gas in the combustion chamber 10a is introduced into the cylinder 20 and the inside of the piston 20 through a gap between the internal wall of the cylinder 10 and the external surface of the piston 20, a gap between the compression ring 22 and the cylinder liner, and the ring groove 23 and a hole 26, in a direction indicated with an arrow of D. This phenomenon also occurs during the explosion stroke (see FIG. 1c), in which the air flows in a direction indicated with an arrow C. The cause of this problem mainly resides on the oil ring and the space between the ring grooves through which the exhaust and the suction occur.
More detailed description of this will be made with reference to FIGS. 2a and 2b. 
FIG. 2a shows the kinds of the oil rings which may be mounted around the piston; and FIG. 2b represents a sectional view of a state of the oil ring mounted on a one piece piston, while FIG. 2c being an enlarged sectional view of the oil ring shown in FIG. 2b. 
As shown in FIG. 2a, the oil ring has through-holes 24c formed through a center of the oil ring 24 and a pair of protrusions 24a and 24b protruding along a circumferential direction on an external surface of the oil ring 24 and being separated from each other. The protrusions serve to scratch the engine oil adhering to the internal wall of the cylinder liner during the reciprocating movements of the piston. The lower protrusion 24b firstly scratches down the oil adhering to the internal wall of the cylinder liner, while the upper protrusion 24a further scratches down the oil remaining thereon, providing a dual performance in scratching the oil.
As shown in FIG. 2b, the oil scratched down by the oil ring 24 is introduced into the through-hole 24c to flow into the inside 20b of the piston via the hole 26 communicating with the inside 20b of the piston.
As shown in FIGS. 2a through 2c, the oil ring 24 may have a ring-shaped spring 29 mounted therein. However, the ring-shaped spring 29 equipped in the oil ring makes a space between the oil ring and the ring groove 23. Accordingly, a certain amount of oil will be kept within the ring groove 23.
That is, during the reciprocating movements of the piston as shown in FIGS. 1a through 1d, especially, when the piston moves down from the top dead point to the bottom dead point, the internal pressure is instantaneously generated in the piston due to the inertia of the air within the piston and then the oil remaining in the ring groove and the oil sticking to the internal wall of the cylinder liner are drawn to flow conversely into the combustion chamber 10a, going against the oil ring 24 along the internal wall of the piston liner.
In this regard, developments for an oil ring capable of providing a strong air-tight condition between the oil ring 24 and the ring groove 23, thereby reducing the communication between both sides of the oil ring and efficiently removing the oil adhering to the internal wall of the cylinder liner has been requested. Particularly, in case of the one-piece piston, since it is made by using casting, being accompanied by a lot of limitations, the development of the oil ring capable of providing the strong air-tight is needed strongly. That is, the oil-air keeping ring insulating the air from the oil and being capable of efficiently removing the oil is necessary.
Further, since a dividable piston made in such a manner that an upper portion of the piston is firstly made of a heat-resistant material and then it is assembled with a piston body may be employed as a piston of the internal combustion engine, an oil ring fit for the dividable piston or a piston having a reverse-flow thwarting construction has been requested.
It is an object of the present invention to provide a one piece piston assembly for use in an internal combustion engine, having an oil ring fit for a one piece piston, an oil discharge construction and a reverse-flow thwarting construction, in order to prevent a reverse flow of the oil.
Another object of the present invention is to provide a dividable piston having an enhanced reverse flow thwarting construction in order to prevent a reverse flow of the oil or a reverse flow of fuel in the combustion chamber or combustion gas into the engine oil.
To achieve the above and other objects, the present invention provides a one piece piston for use in an internal combustion engine provided with a plurality of compression rings and oil rings on its circumferential surface includes ring grooves having a hole communicating with an inside of the piston, oil rings received in the ring grooves, respectively; and a keeping ring mounted between the oil rings and having on its internal surface a spring receiving groove whose inner diameter is larger than an outer diameter of a ring type spring, wherein a separation between an external surface of the ring groove and the internal surface of the keeping ring is maintained equal to that of the compression ring and a hole is formed to allow the ring groove to communicate with the inside of the piston.
The keeping ring has a shape similar to a taper under cut type compression ring, in which a spring receiving groove having a diameter larger than the diameter of the ring type spring is formed on an inner peripheral surface, the ring type spring being received in the spring receiving groove.
The keeping ring is provided with on its upper and lower sides a pair of protrusions, respectively, and through holes separated from one another in a predetermined distance along a circumferential direction on an external surface of the keeping ring, the keeping ring having on its inner peripheral surface a spring receiving groove in which said ring type spring is received.
In accordance with the present invention, there is provided a dividable piston for use in an internal combustion engine having a crown whose upper side is made of heat resisting material, and a piston body provided with a plurality of compression rings and oil rings on its circumferential surface, the piston characterized in that: a hole is formed through a lower circumferential surface of the crown to allowing a ring groove into which said oil ring is inserted to communicate with an internal surface of the crown, wherein oil introduced into the ring groove by the oil ring is drained along an oil passageway via the hole; and a semi-circular protrusion is symmetrically made by partially cutting portions near a pin hole and an oil passageway communicating with the holes is formed through a body of the piston, the oil passageway also communicating with a plurality of holes formed radially inwardly from the upper peripheral surface of the piston body and a drain hole positioned vertically.
The oil ring is provided with on its upper and lower sides a pair of protrusions, respectively, and through holes separated from one another in a predetermined distance along a circumferential direction on an external surface of the oil ring, the keeping ring having on its inner peripheral surface a spring receiving groove in which said ring type spring is received.
The oil ring is provided with a spring receiving groove having a diameter larger than the diameter of the ring type spring is formed on an inner peripheral surface, the ring type spring being received in the spring receiving groove.
A keeping ring may be mounted between the compression ring and the oil ring of the crown.